An American doctor working as a missionary in Liberia has tested positive for Ebola, says SIM (Serving In Mission), an international Christian ministry organization.

The doctor, who remains unidentified, was treating obstetrics patients at SIM’s ELWA hospital in Monrovia, but was not working directly with Ebola patients. It’s unknown how he contracted the virus because the Ebola ward isn’t in the same facility, according to SIM, which has a 136-acre campus in the Liberian capital.

My heart was deeply saddened, but my faith was not shaken, when I learned another of our missionary doctors contracted Ebola,” said Bruce Johnson, president of SIM USA.

SIM says the doctor is “doing well and is in good spirits.”

It was not yet immediately confirmed if the American doctor will be transported back to the U.S. for treatment.

This makes the third American missionary to contract the virus. Two other American aid workers who were stationed in West Africa tested positive for Ebola and were transported back to the U.S. for treatment. Both patients were discharged last month after 19 days in isolation in an Atlanta hospital.

Ebola has killed more than 1,500 people in Sierra Leone, Guinea, Liberia and Nigeria and has now appeared in a fifth West African country, Senegal, in the worst outbreak ever recorded. Ebola has a fatality rate of up to 90%.

The international group Doctor Without Borders warned Tuesday that the world is ‘losing the battle’ against Ebola, while U.N. officials implored all countries to quickly step up their response by contributing health experts and other help.

SIM is an international organization that is based in North Carolina. It employees nearly 3,000 workers in more than 65 countries. The Christian ministry focuses on education, community development and public health.

Additional information in this report was provided by the Associated Press.